67 research outputs found
Numerical evaluation of the ferrofluid behaviour under the influence of three-dimensional non-uniform magnetic field
Investigating the effects of a non - uniform magnetic field on heat and flow characteristics of a ferrofluid
Review on the conversion of thermoacoustic power into electricity
Thermoacoustic engines convert heat energy into high amplitude acoustic waves
and subsequently into electric power. This article provides a review of the
four main methods to convert the (thermo)acoustic power into electricity.
First, loudspeakers and linear alternators are discussed in a section on
electromagnetic devices. This is followed by sections on piezoelectric
transducers, magnetohydrodynamic generators, and bidirectional turbines. Each
segment provides a literature review of the given technology for the field of
thermoacoustics, focusing on possible configurations, operating
characteristics, output performance, and analytical and numerical methods to
study the devices. This information is used as an input to discuss the
performance and feasibility of each method, and to identify challenges that
should be overcome for a more successful implementation in thermoacoustic
engines. The work is concluded by a comparison of the four technologies,
concentrating on the possible areas of application, the conversion efficiency,
maximum electrical power output and more generally the suggested focus for
future work in the field.Comment: The following article appeared in J. Acoust. Soc. Am 143(2) and the
final version in a proper two-column format may be found at:
http://scitation.aip.org/content/asa/journal/jasa/143/2/10.1121/1.502339
Computational fluid dynamics analysis of the oscillatory flow in a jet pump: the influence of taper angle
A two-dimensional CFD model for predicting the oscillating flow through a jet pump
is developed. Various taper angles are investigated and total minor loss coefficients are derived.
A good correspondence is achieved with experimental results from the literature. However, at
higher taper angles a dramatic decay in the jet pump pressure drop is observed, which serves
as a starting point for the improvement of jet pump design criteria for compact thermoacoustic
application
Jet pumps for thermoacoustic applications: design guidelines based on a numerical parameter study
The oscillatory flow through tapered cylindrical tube sections (jet pumps) is
characterized by a numerical parameter study. The shape of a jet pump results
in asymmetric hydrodynamic end effects which cause a time-averaged pressure
drop to occur under oscillatory flow conditions. Hence, jet pumps are used as
streaming suppressors in closed-loop thermoacoustic devices. A two-dimensional
axisymmetric computational fluid dynamics model is used to calculate the
performance of a large number of conical jet pump geometries in terms of
time-averaged pressure drop and acoustic power dissipation. The investigated
geometrical parameters include the jet pump length, taper angle, waist diameter
and waist curvature. In correspondence with previous work, four flow regimes
are observed which characterize the jet pump performance and dimensionless
parameters are introduced to scale the performance of the various jet pump
geometries. The simulation results are compared to an existing quasi-steady
theory and it is shown that this theory is only applicable in a small operation
region. Based on the scaling parameters, an optimum operation region is defined
and design guidelines are proposed which can be directly used for future jet
pump design.Comment: The following article has been accepted by the Journal of the
Acoustical Society of America. After it is published, it will be found at
http://scitation.aip.org/JAS
A numerical investigation on the vortex formation and flow separation of the oscillatory flow in jet pumps
A two-dimensional computational fluid dynamics model is used to predict the
oscillatory flow through a tapered cylindrical tube section (jet pump) placed
in a larger outer tube. Due to the shape of the jet pump, there will exist an
asymmetry in the hydrodynamic end effects which will cause a time-averaged
pressure drop to occur that can be used to cancel Gedeon streaming in a
closed-loop thermoacoustic device. The performance of two jet pump geometries
with different taper angles is investigated. A specific time-domain impedance
boundary condition is implemented in order to simulate traveling acoustic wave
conditions. It is shown that by scaling the acoustic displacement amplitude to
the jet pump dimensions, similar minor losses are observed independent of the
jet pump geometry. Four different flow regimes are distinguished and the
observed flow phenomena are related to the jet pump performance. The simulated
jet pump performance is compared to an existing quasi-steady approximation
which is shown to only be valid for small displacement amplitudes compared to
the jet pump length.Comment: The following article has been accepted by the Journal of the
Acoustical Society of America. After it is published, it will be found at:
http://scitation.aip.org/JAS
Different effects of continuous infusion of interleukin-1 and interleukin-6 on the hypothalamic-hypophysial-thyroid axis
The cytokines interleukin-1 (IL-1) and IL-6 are thought to be important
mediators in the suppression of thyroid function during nonthyroidal
illness. In this study we compared the effects of IL-1 and IL-6 infusion
on the hypothalamus-pituitary-thyroid axis in rats. Cytokines were
administered by continuous ip infusion of 4 micrograms IL-1 alpha/day for
1, 2, or 7 days or of 15 micrograms IL-6/day for 7 days. Body weight and
temperature, food and water intake, and plasma TSH, T4, free T4 (FT4), T3,
and corticosterone levels were measured daily, and hypothalamic pro-TRH
messenger RNA (mRNA) and hypophysial TSH beta mRNA were determined after
termination of the experiments. Compared with saline-treated controls,
infusion of IL-1, but not of IL-6, produced a transient decrease in food
and water intake, a transient increase in body temperature, and a
prolonged decrease in body weight. Both cytokines caused transient
decreases in plasma TSH and T4, which were greater and more prolonged with
IL-1 than with IL-6, whereas they effected similar transient increases in
the plasma FT4 fraction. Infusion with IL-1, but not IL-6, also induced
transient decreases in plasma FT4 and T3 and a transient increase in
plasma corticosterone. Hypothalamic pro-TRH mRNA was significantly
decreased (-73%) after 7 days, but not after 1 or 2 days, of IL-1 infusion
and was unaffected by IL-6 infusion. Hypophysial TSH beta mRNA was
significantly decreased after 2 (-62%) and 7 (-62%) days, but not after 1
day, of IL-1 infusion and was unaffected by IL-6 infusion. These results
are in agreement with previous findings that IL-1, more so than IL-6,
directly inhibits thyroid hormone production. They also indicate that IL-1
and IL-6 both decrease plasma T4 binding. Furthermore, both cytokines
induce an acute and dramatic decrease in plasma TSH before (IL-1) or even
without (IL-6) a decrease in hypothalamic pro-TRH mRNA or hypophysial TSH
beta mRNA, suggesting that the acute decrease in TSH secretion is not
caused by decreased pro-TRH and TSH beta gene expression. The
TSH-suppressive effect of IL-6, either administered as such or induced by
IL-1 infusion, may be due to a direct effect on the thyrotroph, whereas
additional effects of IL-1 may involve changes in the hypothalamic release
of somatostatin or TRH.(ABSTRACT TRUNCATED AT 400 WORDS
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